High temperature superconducting (HTSC) compounds including mixed oxides of rare earth, alkaline earth and copper metals are known. For example, Wu et al., Physical Review Letters, Vol. 58, No. 9, pp. 908-910 (1987) and Hor et al., Physical Review Letters, Vol. 58, No. 9, pp. 911-912 (1987) have disclosed Y-Ba-Cu-O compound systems as exhibiting superconductivity. Additionally, in Physical Review Letters, Vol. 58, No. 18 (1987), Moodenbaugh et al. (pp. 1885-1887), Murphy et al. (pp. 1889-1890) and Hor et al. (pp. 1891-1894) disclose additional rare earth, alkaline earth, copper metal mixed oxide compounds exhibiting superconductive properties. Generally, these references disclose the formation of the rare earth, alkaline earth, copper metal mixed oxide compounds by sintering individual oxide powders.
Additional superconducting mixed metal oxide compounds of La-Sr-Cu--O, Bi-Sr-Ca-Cu--O and Tl-Ba-Ca-Cu--O have also been developed. For example, Tarascon et al., Physical Review B, Vol. 38, No. 13, pp. 8885-8892 (1988) disclose Bi-Sr-Ca-Cu--O superconducting compounds of the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.y wherein n= 1, 2 or 3 which are prepared by firing at high temperatures stoichiometric amounts of Bi.sub.2 O.sub.3, SrCO.sub.3 or SrO.sub.2, and CuO powders. Similarly, Chakoumakos et al., Journal of Materials Research, Vol. 4, No. 4, p. 767 (1989), have disclosed the preparation of Br-Sr-Cu--O compounds, particularly Bi.sub.2 Sr.sub.2 CuO.sub.6 using ceramic processing and melt crystallization techniques.
Schlom et al., Proceedings of MRS Meeting, Boston, 1989, and article accepted for publication in Journal of Crystal Growth, have disclosed Bi-Sr-Ca-Cu--O compounds of the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x wherein n is from 1 to 5 which are formed by molecular beam epitaxy of layered structures. Eckstein et al., Proceedings of the International Superconductivity Electronics Conference, Tokyo, 1989, have also disclosed the formation of thin films of perovskite-related high-temperature superconductors using atomic layer molecular beam epitaxy. The preparation of superconducting compounds of the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.y is further disclosed by Nakayama et al., Japanese Journal of Applied Physics, Vol. 28, No 10, pp. L1809-L1811 (October 1989), using molecular beam epitaxy techniques with shutter control, while Fujita et al., Applied Physics Letters, Vol. 56, No. 3, pp. 295-297 (Jan. 15, 1990), disclose the preparation of superconducting compounds of the formula Bi.sub.2 (SrCa).sub.3 Cu.sub.2 O.sub.x by epitaxial growth techniques employing ion beam sputtering with an atomic oxygen source.
Although it is believed that a reduction in the number of Bi atoms per unit cell of the crystal structure in known Bi-Sr-Ca-Cu--O superconducting compounds would increase the conductivity of such compounds, attempts to synthesize Bi.sub.1 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x materials, largely inspired by the discovery of Tl.sub.1 Bl.sub.2 Ca.sub.3 Cu.sub.4 O.sub.x compounds, have failed. Prior to the present Invention, it has generally been believed that such compounds are unstable and therefore impossible to form.